Video monitors used in computer display systems provide an output device such as a cathode ray tube or diode display matrix which are horizontally and vertically scanned in a raster pattern similar to that utilized in television receivers. The to-be-displayed information is coupled to the display in synchronism with the scanning process. In cathode ray tubes, for example, the electron beams within the cathode ray tube are intensity modulated with the to-be-displayed video signals in synchronism with the beam scanning process.
In most computer display systems, the computer develops horizontal and vertical scan synchronizing signals which are appropriately related to the to-be-displayed information. Within the video monitor, horizontal and vertical scanning systems respond to and are controlled by these synchronizing signals.
In many video monitors, additional information beyond scanning system synchronization may be communicated between the computer and the video monitor using the scan synchronizing signals. In such systems, the computer produces a set of horizontal and vertical scan synchronizing signals having signal frequencies and polarities established in a selected combination which identifies and communicates certain display system information. Within the video monitor, a so-called front end processor utilizes the horizontal and vertical scan synchronizing information to establish monitor display mode (for example, number of pixels per line, number of lines per frame, etc.). In addition, the front end processor also affects certain display system adjustments such as display size and horizontal and vertical centering.
In order to reliably communicate such information using synchronizing signal polarities and frequencies, the computer applies a predetermined combination of synchronizing signal polarities and frequencies to the video monitor. Within the video monitor, the front end processor "decodes" the relevant information and processes it to implement corresponding display mode characteristics and operation. The proper function of such video monitor systems requires that the display mode and adjustment information be accurately recovered while the integrity of the synchronizing signals is maintained to avoid interfering with the basic scan synchronizing process. As a result, the systems heretofore provided within video display monitors for recovering such information have often become excessively complex and costly. In addition, display system performance has, in some instances, been compromised.
It is an object, therefore, of the present invention to provide an improved video monitor. It is a more particular object of the present invention to provide an improved synchronizing signal front end processor for use in a video monitor.